Ceramic material and method of producing the same



limited States atent Ofiiice Patented July 26, 1960 CERAMIC MATERIAL ANDNIETHOD OF PRODUCING THE SAME John M. Herbert, Horton, England, assignorto The Plessey Company Limited, Ilford, England, a British company NoDrawing. Filed May 7, 1956, Ser. No. 582,945

Claims. (Cl. 317258) This invention relates to ceramic materials and isconcerned with the manufacture of a ceramic material of highpermittivity suitable for use as a condenser dielectric.

It is an object of the invention to provide an improved ceramicdielectric material which facilitates the application of electrodes madeof a base metal in the same operation with the sintering of thedielectric. Another object is to provide an improved ceramic dielectricmaterial which when fired in a reducing atmosphere will yield a sintereddielectric ceramic body of high permittivity, suitable for use as acondenser dielectric. Other objects and features of the invention willappear as this specification proceeds.

gredients in hydrogen. Preferably the ingredients are in the proportionsrequired to give 2BaTiO MnO,

4BaTiO MnO or 6BaTiO MnO although it is doubtful if such mixed which isbelieved to be a solution of manganous oxide in barium titanate.

It is possible to substitute other elements for up to 50 mol percent ofthe barium and titanium. Substitutions of more than a few percent resultin a material of reduced permittivity, but it may have a lowertemperature coefiicient of permittivity. Elements which may be subvstituted for barium are magnesium, beryllium, calcium, strontium,yttrium and lanthanum. For titanium there may be substituted zirconium,hafnium cerium, thorium, tin and tantalum. I

Magnesium may be used in part instead of manganese, substitution of upto 75 mol percent being possible without appreciably affecting thedielectric properties.

Although the dielectric is slightly inferior in electrical propertieswhen compared with ceramic compositions fired in air, it is quitesuitable for smoothing condensers and the like and the invention makespossible and economical manufacture of condensers of large capacitance(say 8 mi.) with a high permittivity ceramic dielectric.

An advantage of the invention is that it is possible for base metalelectrodes to be sintered simultaneously with the firing of the ceramiccomposition; any metal can be used which does not react with bariumtitanate or melt below 1150 C.

In order that the invention may be more fully and clearly understoodvarious ways of putting the invention into effect will now be described.

Three possible compositions for the dielectric material, which will forconvenience be referred to as A, B and C, are given below, theproportions being by weight:

oxides exist. The material contains free manganous oxide and a compoundclosely resembling barium titanate and A B O Barium carbonate..- 118. 4130. 0. 130. 0 Titanium dioxide.-- 47. 9 52. 6 51. 3 Manganese carbonate34. 5 19.0 37. 9 Zirconium dioxide 2, 03

' The ingredients in the form of fine powders produced by precipitation,are thoroughly mixed and then fired in air at 1100" C. for two hours.The resulting mass is In the case of composition D, the powderedingredients arewell mixed, fired in air at 1000 C. for two hours andthen ground; compositions E and F are simply mixtures of powders.

Further dielectric compositions in accordance with the invention aretabulated below where molecular percentages of the various ingredientsare shown. It will be noted that examples of compositions in which partof the titanium is replaced by otherelements are included.

Composition BaO TiOglMno Th0; CeO; ZrO; S1102 T8205 G 46.3 H 40.0 .T'.40.0 K 40:0 L 40.0 M 40.0

. It is possible to produce electrodes by including any of the followingelements in the dielectric composition,

' so that conductive particles are dispersed throughout the dielectric:copper, silver, gold, lead, antimony, bismuth, molybdenum, tungsten,iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium andplatinum. If chromium or niobium are included in the compositionthen1conductive oxides of these elements are formed.

The following elements are relatively inert and their oxides if presentin the compositions merely result in a lowering of the dielectricconstant: lithium, sodium, potassium, rubidium, caesium, boron,aluminium, silicon, and phosphorous.

- The presence of zinc, cadmium, mercury, or arsenic in the compositionhas no effect in the dielectric properties since the oxides of theseelements will be reduced and will then volatilise. Fluorine and sulphurform innocuous anions and also have no ellect on the properties.

In the construction of capacitors, it is often advantageous to have theelectrodes and dielectric in the form of films, and for this purpose theabove compositions can be mixed with a binding lacquer. A suitablelacquer comprises cellulose acetobutyrate, diamyl tartarate, andethylene dichloride in the proportions by weight of 9, 5 and 50respectively. parts of lacquer are thoroughly" mixed with 180 parts of apowdered dielectric or electrode composition. The semi fluid mass thusproduced] is spread in a uniform thin layer on a smooth surface,

3 After drying, the resulting filin is peeled from the surface and cutinto pieces of the required size and shape.

One way in which the above compositions can be used to construct acapacitor, is to assemble alternate pieces of The sintered'capacitorassemblies require the attachment of leads and to be coated with aninsulating medium to protect them from the atmosphere. In the case ofelectrode composition E wires may be hard or soft dielectric andelectrode film made as described above, to 5 soldered to the sinteredparts. In the case of D and F form a stack of interleaved-parts. Thepieces of film are direct soldering is diflicult though the exposedparts of caused to adhere together by applying pressure (0.5 ton theelectrodes may be electroplated and then soldered. per sq. in.) at atemperature of 120 C. The electrode Leads can be attached with a pasteof glass and iron films can be joined together by painting the gapsbetween powders which is heated so as to melt the glass; this their proecting ends with a suspension of one of the operation can be combinedwith the application of a electrode compositions. coating of glass; tothe whole assembly.

If an electrode composition such as D which is free Dielectrics whenprepared from compositions A, B and of metal is used in the aboveconstruction, the assembled C by the above methods have the propertiestabulated stack can be fired at 500-1000 C. in air to remove all below:organic matter. Thereafter, it has to be fired in are during" atmospheres'tih as hydrogen at 1150" C. for two ho rs in order to mature theceramic dielectric and to A B G r tlllje and Slnfef flie leCffOdS 'clempmg Di 1. P- D 1 ,P D1 1 P If compos1t1on E or is used the entire firngprocess m6 Factor, Factor, trio Factor, can be conveniently carned outin a reducing atmosphere. Constant Percent Constant Percent ConstantPercent The carbonaceous residueof the plastic binder can be. p 1.eliminated by introducing a small amount of carbon 27 4,200 3.0 3,200 0.75 oxide or water into the furnace atmosphereat a temperag: 8: turesomewhat below that at which sintering takes place. 2. 1 4, 27% 2.72,520 0.75 For instance, when the furnace temperature reaches 1000 i: i:3 e i 38 3; C. the hydrogen supply used as the reducing atmosphere 1.83,340 as 1, 050 1.00 c' 1.8 2,800 3.4 1,410 1.00 is passed through avessel contaimng water at 70 C. L9 2,1400 36 1,260 L02 before it entersthe furnace. The gas picks up suflicient e e a a water vapour in thisway to oxidise any carbon but not i A V 7 V V enough to oxidise metalliciron. After an hour at 1000" Compositions G, H, J, K, L and M have thefollowmg C. the furnace is heated to the sintering temperature,properties:

f o n J V K L M Temperw ature, C. Dielec- Power Dielec- Power Dielec-Power Dlelee- Power Dlelec- Power Dlelec Power trlc Factor, tric Factor,tric' Factor, ie .liactor, ,tric, I Factor, trio Factor, ConstantPercent Constant Percent Constant Percent Constant Percent ConstantPercent Constant Percent 1-l50 C., the water is removed from the gascircuit and 4 the sintering completed in dry hydrogen.

'Another manner of constructing a capacitor is to take pieces ofdielectric film, oxidisethem fre'e'of organic mat ter and then fire inhydrogen. These piecesmay' then be coated witha suspension of iron andglass powders cone taining riot more'than 3 parts of powderedglassto'one of iron;- the glass'is matched in coefiicient'of thermalexpansion'to'the iron andthe titanate composition. The coated pieces areinterleaved and any end connections madewith the-iron-glass suspension;Theassemblies are then fired in hydrogen to asufdciently hightemperature to sinter the glass.

The advantage of' the method in this case liesin' the cheapnessof-theiron and glass electrode material which may be applied thickly tothe dielectric pieces so that,- on sintering, it will fill the spaceswhich would otherwise be present due to the lack of perfect flatness ofthe dielectric layers. a

The dielectrica'nd electrodematerials can also be extruded' as ribbonandwou'nd together in a similar manner to paper condensers, andthen-subsequently sintered;

The dielectric may be pressed as a compact from powder with or without asuitable binder and combined either with similar compacts of electrodematerial or with the electrode material combined in aplastic bound-film.

The electrode may also be in the form of a metallic wire which iscoated" with the powdered dielectric material. The dielectric issintered in hydrogen toiform anadherent-enamel. Air outer electrode mayeither be applied subsequently or as a -r'urther coating; prior toSintering:

What I claim is:

l. A method of producing a dielectric sintered body, which comprisesshaping the body ofa material which, atleast after sintering consistsessentially, of barium titanate and a smaller molecular quantity ofmanganous oxide-,=t he amount of'manganous oxide being at leastapproximately 14 mol percent of the composition as a Whole, andsintering said body in a reducing atmosphere to give a bodywhichcomprises barium titanate" and manganous oxide in a proportioncorresponding to a formula selected from the group consisting of MnO.(BaTiG M110. (*BaTiOgh and MnOZCBaT-iO 6 2. A sintered body as claimedin'claim' 1, wherein a portion not'exceeding three quarters of themolecular manganous oxide'contentis replaced by magnesium oxide. 3. Aceramic capacitor comprising an integral sintered body including atleast one layer'of ceramic dielectric material whichniaterial-consistsessentially of' bariu'm titanate. anda-smaller molecular quantity ofmanganousioxide,

in said integral sintered body includes a plurality of--lay-' ers ofsuch ceramic dielectric material and electrodes of such basemetalseparatingsaid layers of dielectric'n'iw' terial.

5. A ceramic capacitor as claimed in claim 3, wherein a portion of themanganous oxide is replaced by magnesium oxide, the molecular magnesiumoxide content being not more than three times the molecular manganousoxide content.

References Cited in the file of this patent UNITED STATES PATENTS Fuwaet al Nov. 15, 1938 Roup et al Aug. 29, 1950 Wentworth Nov. 14, 1950

1. A METHOD OF PRODUCING A DIELECTRIC SINTERED BODY, WHICH COMPRISESSHAPING THE BODY OF A MATERIAL WHICH, AT LEAST AFTER SINTERING CONSISTSESSENTIALLY OF BARIUM TITANATE AND A SMALLER MOLECULAR QUANTITY OFMANGANOUS OXIDE, THE AMOUNT OF MANGANOUS OXIDE BEING AT LEASTAPPROXIMATELY 14 MOL PERCENT OF THE COMPOSITION AS A WHOLE, ANDSINTERING SAID BODY IN A REDUCING ATMOSPHERE TO GIVE A BODY WHICHCOMPRISES BARIUM TITANATE AND MANGANOUS OXIDE IN A PROPORTIONCORRESPONDINGG TO A FORMULA SELECTED FROM THE GROUP CONSISTING OF